You’re working on a project at work, and you hear the “bing” of Mail, telling you there’s a new e-mail. You are confronted with the question, “Do I stop what I’m doing and see if the e-mail is important, or do I take a chance and keep working on my project?”

What if you didn’t have to? What if a little box popped up on the side of your screen with a summary of the e-mail, giving you a short-term look at the e-mail so you can decide if it’s important or not?
Believe it or not, the software that does that is already here. And it’s free (donations are accepted).
It’s called Growl. Growl is a notification system for Mac OS X: it allows applications that support Growl to send you notifications (took the description right off their web site because I couldn’t have said it better myself).

I had heard of Growl, but didn’t see much use for it until I accidentally installed it. Yes, I accidentally installed Growl. I don’t even know what program installed it for me (which I don’t like, but I seem to recall an installer asking me if I wanted to install Growl, so I must have said “yes.”)
Anyway, all of a sudden, I started seeing notifications when my RSS reader, the open-source Vienna, downloaded new articles. Thought that was pretty handy. I could tell when there were new articles without bumping down to the bottom of the screen and making the dock appear (Vienna has a number notifier in its dock icon and I keep my dock hidden). Saves time.
So I started investigating and found Growl in my System Preferences (in the Other category at the bottom). After some exploration, I found that there is a plugin for Apple’s Mail program that allows Growl to notify you of new e-mail.

And there are a whole bunch of other programs that are either written to work with Growl, and for some others there are plugins.

But the one that really helps me is the Mail plugin. My day job is at a newspaper. I do page design for my home paper and tech support for several other papers. As part of that, I get an enormous amount of e-mail from the Associated Press. Most of if deals with their web-based video network, and for some reason, they can’t just send me the important stuff, they send me an email every time they post a new video.

I have them whisked off to a folder in Mail, but it “bing”s every time one of those e-mails come in and I don’t always have time to see whether or not it’s important. But I want to know immediately if someone is having a problem related to their deadlines.
Growl shows me who the email is from and allows me to more-easily ignore the AP stuff.
And that’s just one example. I also use Semulov, which unmounts volumes. Now when a volume unmounts, I see it in a Growl notification.
I’m sure you can come up with many other uses, but I just wanted to introduce you to this cool little program.